The present invention relates generally to electroactive polymers that convert between electrical energy and mechanical energy. More particularly, the present invention relates to polymers and their use as generators, sensors, in actuators and various applications. The present invention also relates to additives added to a polymer, laminates comprising a transducer and methods of fabricating transducer.
In many applications, it is desirable to convert between electrical energy and mechanical energy. Exemplary applications requiring translation from electrical to mechanical energy include robotics, pumps, speakers, general automation, disk drives and prosthetic devices. These applications include one or more actuators that convert electrical energy into mechanical workxe2x80x94on a macroscopic or microscopic level. Common electric actuator technologies, such as electromagnetic motors and solenoids, are not suitable for many of these applications, e.g., when the required device size is small (e.g., micro or mesoscale machines). Exemplary applications requiring translation from mechanical to electrical energy include mechanical property sensors and heel strike generators. These applications include one or more transducers that convert mechanical energy into electrical energy. Common electric generator technologies, such as electromagnetic generators, are also not suitable for many of these applications, e.g., when the required device size is small (e.g., in a person""s shoe). These technologies are also not ideal when a large number of devices must be integrated into a single structure or under various performance conditions such as when high power density output is required at relatively low frequencies.
Several xe2x80x98smart materialsxe2x80x99 have been used to convert between electrical and mechanical energy with limited success. These smart materials include piezoelectric ceramics, shape memory alloys and magnetostrictive materials. However, each smart material has a number of limitations that prevent its broad usage. Certain piezoelectric ceramics, such as lead zirconium titanate (PZT), have been used to convert electrical to mechanical energy. While having suitable efficiency for a few applications, these piezoelectric ceramics are typically limited to a strain below about 1.6 percent and are often not suitable for applications requiring greater strains than this. In addition, the high density of these materials often eliminates them from applications requiring low weight. Irradiated polyvinylidene difluoride (PVDF) is an electroactive polymer reported to have a strain of up to 4 percent when converting from electrical to mechanical energy. Similar to the piezoelectric ceramics, the PVDF is often not suitable for applications requiring strains greater than 4 percent. Shape memory alloys, such as nitinol, are capable of large strains and force outputs. These shape memory alloys have been limited from broad use by unacceptable energy efficiency, poor response time and prohibitive cost.
In addition to the performance limitations of piezoelectric ceramics and irradiated PVDF, their fabrication often presents a barrier to acceptability. Single crystal piezoelectric ceramics must be grown at high temperatures coupled with a very slow cooling down process. Irradiated PVDF must be exposed to an electron beam for processing. Both these processes are expensive and complex and may limit acceptability of these materials.
In view of the foregoing, alternative devices that convert between electrical and mechanical energy would be desirable.
In one aspect, the present invention relates to polymers that convert between electrical and mechanical energy. When a voltage is applied to electrodes contacting a pre-strained polymer, the polymer deflects. This deflection may be used to do mechanical work. Similarly, when the polymer deflects, an electric field is produced in the polymer. This electric field may be used to produce electrical energy. Some polymers of the present invention include additives that improve conversion between electrical and mechanical energy. Other polymers of the present invention include laminate layers that improve conversion between electrical and mechanical energy.
Some polymers of the present invention are pre-strained. The pre-strain improves the mechanical response of an electroactive polymer relative to a non-strained polymer. The pre-strain may vary in different directions of a polymer to vary response of the polymer to the applied voltage.
In one aspect, the present invention relates to generators and actuators comprising an electroactive polymer and mechanical coupling to convert between mechanical and electrical energy. Several generators and actuators include structures that improve the performance of an electroactive polymer.
In another aspect, the present invention relates to compliant electrodes that conform to the changing shape of a polymer. Many of the electrodes are capable of maintaining electrical communication at the high deflections encountered with pre-strained polymers of the present invention. In some embodiments, electrode compliance may vary with direction.
In yet another aspect, the present invention provides methods for fabricating electromechanical devices comprising one or more electroactive polymers. Additives that improve conversion between electrical and mechanical energy may be added during fabrication. Polymers of the present invention may be made by casting, dipping, spin coating, spraying or other known processes for fabrication of thin polymer layers.
In still another aspect, the invention relates to a generator for converting mechanical energy to electrical energy. The generator comprising at least two electrodes. The transducer also comprising a polymer arranged in a manner which causes a change in electric field in response to a deflection applied to a first portion of the polymer, wherein a second portion of the polymer is elastically pre-strained.
In another aspect, the invention relates to a generator for converting mechanical energy to electrical energy. The generator comprising at least two electrodes. The transducer also comprising a polymer having a substantially constant thickness and an area orthogonal to the thickness, the polymer arranged in a manner which causes a change in electric field in response to a net area decrease of the polymer for the area orthogonal to the thickness.
In still another aspect, the invention relates to a generator for converting from electrical energy to mechanical energy. The generator comprising at least one transducer, each transducer comprising at least two electrodes and a polymer arranged in a manner which causes a change in electric field in response to a deflection applied to a first portion of the polymer. The generator also comprising a frame attached to a second portion of the polymer, the frame comprising at least one aperture, wherein the first portion of the polymer is arranged in a manner which causes a change in electric field in response to a deflection applied to a third portion of the polymer.
In yet another aspect, the invention relates to a generator for converting mechanical energy in a first direction into electrical energy. The generator comprising at least one transducer, each transducer comprising at least two electrodes and a polymer arranged in a manner which causes a change in electric field in response to a deflection in the first direction. The generator also comprising a flexible frame coupled to the polymer, the frame providing improved conversion from mechanical to electrical energy for the at least one transducer.
In another aspect, the invention relates to a generator for converting mechanical energy in a first direction into electrical energy. The generator comprising at least one transducer, each transducer comprising at least two electrodes and a polymer arranged in a manner which causes a change in electric field in response to a deflection in the first direction. The generator also comprising at least one stiff member coupled to the at least one transducer, the at least one stiff member substantially preventing displacement in a second direction.
In still another aspect, the invention relates to a transducer for converting between mechanical and electrical energy. The transducer comprising at least two electrodes and a polymer arranged in a manner which causes a portion of the polymer to deflect in response to a change in electric field and/or arranged in a manner which causes a change in electric field in response to deflection of the polymer, wherein the polymer includes an additive.
In yet another aspect, the invention relates to a transducer for converting between mechanical and electrical energy. The transducer comprising at least two electrodes and a polymer arranged in a manner which causes a portion of the polymer to deflect in response to a change in electric field and/or arranged in a manner which causes a change in electric field in response to deflection of the polymer, wherein the polymer comprises a monoethylenically unsaturated monomer homopolymerizable to form a polymer having a glass transition temperature less than about 0 degrees Celsius.
In another aspect, the invention relates to a transducer for converting between mechanical and electrical energy. The transducer comprising at least two electrodes and a polymer arranged in a manner which causes a portion of the polymer to deflect in response to a change in electric field and/or arranged in a manner which causes a change in electric field in response to deflection of the polymer, wherein the polymer comprises a thermoplastic elastomer.
In still another aspect, the invention relates to a transducer for converting between mechanical and electrical energy. The transducer comprising at least two electrodes and a polymer arranged in a manner which causes a portion of the polymer to deflect in response to a change in electric field and/or arranged in a manner which causes a change in electric field in response to deflection of the polymer, wherein the polymer comprises silicone and acrylic moieties.
In yet another aspect, the invention relates to a transducer for converting between mechanical and electrical energy. The transducer comprising at least two electrodes and a polymer arranged in a manner which causes a portion of the polymer to deflect in response to a change in electric field and/or to change in electric field in response to deflection. The transducer also comprising a layer laminated to at least a portion of one of the polymer and the at least two electrodes, and mechanically coupled to the polymer and/or one of the at least two electrodes.
In another aspect, the invention relates to a method of fabricating a transducer comprising a polymer comprising an additive and one or more electrodes. The method comprising adding an additive to a polymer. The method also comprising fixing a portion of the polymer to a solid member. The method further comprising forming the one or more electrodes on the polymer.
In still another aspect, the invention relates to a device for converting between electrical energy and mechanical energy. The device comprising at least one transducer, each transducer comprising at least two electrodes and a polymer arranged in a manner which causes a portion of the polymer to deflect in response to a change in electric field and/or arranged in a manner which causes a change in electric field in response to deflection of the polymer. The device also comprising at least one flexure coupled to a second portion of the polymer, the flexure improving conversion between electrical energy and mechanical energy.
In yet another aspect, the invention relates to a device for converting between electrical energy and mechanical energy in a first direction. The device comprising at least one transducer, each transducer comprising at least two electrodes and a polymer arranged in a manner which causes a first portion of the polymer to deflect in the first direction in response to a change in electric field and/or arranged in a manner which causes a change in electric field in response to deflection of the polymer in the first direction. The device also comprising a pair of flexures coupled to opposing sides of the polymer, the pair of flexures improving conversion between electrical energy and mechanical energy in the first direction.
In another aspect, the invention relates to a device for converting between electrical energy and mechanical energy. The device comprising at least one transducer, each transducer comprising at least two electrodes and a polymer arranged in a manner which causes a portion of the polymer to deflect in response to a change in electric field and/or arranged in a manner which causes a change in electric field in response to deflection of the polymer. The device also comprising a frame attached to a second portion of the polymer, the frame comprising at least one non-circular aperture, wherein the first portion of the polymer is arranged in a manner which causes a change in electric field in response to a deflection applied to a portion of the polymer.
These and other features and advantages of the present invention will be described in the following description of the invention and associated figures.